1. Field of the Invention
The present invention relates to an apparatus and method for testing quality of an optical disc, and more particularly, to an apparatus method for testing quality of mechanical endurance of a surface of an optical disc.
2. Discussion of the Related Art
Up to now, there are recording media such as a magnetic recording tape, a laser disc (LD) or a compact disc (CD) as an optical disc, and a digital video disc (DVD) newly born with a vast recording capacity.
Since the optical disc among the recording media utilizes a digital recording system different from the conventional recording system, that is, magnetic recording system, and has a very small volume and weight so that it is efficient and convenient to keep and carry, it is a recent trend for a consumer to prefer the optical disc.
However, even any appliance should be used without any defect, and if there were any problem in quality, then the consumer's reliability for the manufacturer would be decreased.
This causes more serious problem in the optical disc having minute signal characteristics and brings inferior quality originated from the error of thickness of a disc, scratch, deformity, fingerprint, and attachment of foreign material during manufacturing of the product.
Thus, a produced optical disc undergoes the quality test as a next process, and the optical disc is shipped to an optical disc market.
A conventional quality test for an optical disc is generally performed by four measuring drives.
First, under the assumption that characteristics of optical discs manufactured by the same equipment are identical, the manufacturer makes a choice of an arbitrary optical disc from all of the manufactured optical discs and loads the selected optical disc onto a measuring system.
In the first measuring drive, a high frequency wave signal and a jitter are measured by means of a signal reproduced from the optical disc.
In the second measuring drive, a servo signal (a focusing error signal and a tracking error signal) are measured based on a signal reproduced from the optical disc.
In the third measuring drive, the mechanical characteristics of the optical disc, which undergoes the quality test, are measured.
Finally, in the fourth measuring drive, the optical characteristics of the optical disc are measured.
As described above, according to the conventional test, an accuracy of information recording, and the mechanical characteristics and an optical characteristics of the optical disc are inspected.
From these, since a mechanical damage that would occur on an incident surface of an information recording/reproducing laser beam during the use of an high density optical disc, that is, a scratch and the like causes the deterioration of a signal of an optical disc as well as data loss, and in more worse case, brings the recording and/or reproducing of information onto the optical disc impossible, the damage takes the most important portion of the quality test of the optical disc.
Therefor, to prevent this, a protective coating may be formed to enhance the mechanical stiffness or hardness of the surface of the optical disc.
However, after forming the protective coating on the disc surface for this purpose, the mechanical characteristics of the protective coating should be quantized. Namely, there is need to quantize for how long the protective coating endure the scratch which would occur during the use of the optical disc.
There are a pencil hardness test and a taber abrasion test as a test for the quantization of surface-proof of the high-density optical disc.
The pencil hardness test is an estimating method for estimating the scratch at a hardness value corresponding a hardness of the pencil at an instant when the scratch occurs by contacting pencils of which different hardness to the optical disc in a rectilinear motion.
However, the pencil hardness test is a test for generating the scratch by which a human contacts the pencil on the surface of the optical disc, has disadvantages that it is difficult not only to maintain same load continuously, but also to generate the quantization scratch because the scratch does not occur as many as desired.
The taber abrasion test is a test to estimate degree of endurance by uniformly wearing the surface of the optical disc while giving a predetermined load by means of D1004 method of a standard, American Society for Testing and Materials (ASTM) as a kind of an abrasion wheel.
In the conventional taber abrasion testing apparatus, if an optical disc to be scratched is loaded and rotated, a plurality of abrasion wheels having a predetermined weight contact the optical disc at a perpendicular position to the optical disc so that scratch the surface of the optical disc by a uniform load for at least more ten rotation of the optical disc.
At that time, the ASTM defines the load generated from the abrasion wheel less than 9.8 N (1000 gf), and there are several kinds such as CS-10F, CS-10, and CS-17 to be used.
The taber abrasion testing apparatus as described above is an equipment designed for the purpose of not testing the mechanical endurance of the surface of the optical disc by scratching the optical disc, but testing a degree of the scratch of general plastic goods.
Therefore, the scratch occurring by the taber abrasion testing apparatus is remarkably different from the scratch generated when the optical disc is used actually in real life.
Namely, the taber abrasion testing apparatus determines the endurance of the surface of the optical disc by wearing the surface. This is remarkably different from the situation that real-generated scratch is reacted in a drive (for example, an optical disc drive) for driving the optical disc by responding the operation.
Therefore, since the manufacturer determines the quality of the optical disc by his relative determination with his veteran know-how not quantitative classification according to an actual reference standard when to determine the quality of the optical disc poor or good by the taber abrasion testing apparatus, there are a plenty of errors. Moreover, since the scratches generated on the optical disc in real life and by the taber abrasion testing apparatus are different from each other in the shape, a try to determine the optical disc poor or good with only the know-how without absolute reference value makes vast of errors.
As described above, since, up to now, there is not a special method for quantizing generation degree of the scratch in order to test the mechanical endurance of the surface of the optical disc, a quantization of the degree of the scratch is urgently demanded.